Struggling to locate his blazing sinker, Treinen endured some growing pains in a 3-1 loss to the Pittsburgh Pirates on Thursday night. The right-hander gave up two runs on 5 2/3 innings, striking out four and walking five, with both walks turning into Pittsburgh runs.

“I wasted a lot of pitches,” Treinen said. “I’ve got to cut down on the walks and the try to keep us in the game better by getting out of the situations I’ve been getting myself into.”

Treinen (0-2) retired the first eight batters he faced before running into trouble. He walked Pirates starter Edinson Volquez with two outs in the third, and Volquez came around to score when Treinen hit Andrew McCutchen with an 80 mph changeup. A leadoff walk to Josh Harrison in the fifth ended with Harrison scoring on a sharp single up the middle by McCutchen.

“It was nice to see him go out there and compete,” Washington manager Matt Williams said. “We took him to 100 pitches and he was fine. He threw some good breaking balls and gave us a chance to win but we just didn’t have much offense tonight.”

Ian Desmond hit his eighth homer of the season for the Nationals, but Washington left 10 runners on base. The Nationals have lost three of four.

“There are times during the year where you’re not to score a lot of runs and we’re going through one of those times now, but the runs will come,” Desmond said. “We’ve got too many good hitters in this lineup not to score runs over the long haul.”

Volquez (2-4) limited Washington to just three hits over six innings, helped in part by a pair of spectacular defensive plays. Harrison went flat out to rob Wilson Ramos’ shot to the gap in right-center leading off the ninth and McCutchen made a sliding grab on a sinking liner Anthony Rendon to end the game.

“Our approach was fine,” Williams said. “They made some really nice plays. That happens. It’s big league baseball. They get paid to do that.”

Volquez had been a pleasant surprise during the season’s first month, but scuffled through his previous four starts, going 0-3 with a 10.19 ERA as part of a slide that left Pittsburgh well off the pace in the NL Central a year after making the franchise’s first postseason appearance in more than two decades.

Pirates manager Clint Hurdle wondered if Volquez — who led the National League in walks per nine innings last season — was suddenly throwing too many strikes.

The former All-Star did a better job mixing location and speed against the Nationals. His only real miscue came on a 2-0 fastball in the fourth that Desmond sent into the seats in center field that briefly tied the game at 1.

Treinen, who faced Clayton Kershaw in his previous major league start, wasn’t quite as crisp. He looked stunned after hitting McCutchen.

“It’s frustrating,” Treinen said. “It really bothers me. The last thing you want to do is hit someone with the bases loaded.”

Washington loaded the bases in the eighth off Tony Watson, but the left-hander retired Scott Hairston on a fly to shallow left field to get out of it and Mark Melancon earned his eighth save despite putting two runners on in the ninth.

“That’s what we’re known for, just playing routine baseball, not doing anything too out of the ordinary,” McCutchen said. “(Just) getting in scoring position, getting some runs home and having pitching shut it down for us.”

NOTES: The Pirates claimed right-handed reliever Josh Wall off waivers from the Los Angeles Angels on Thursday and assigned him to Triple-A Indianapolis. Wall is 1-1 with a 15.15 ERA in 15 career major league games. To make room for Wall on the 40-man roster, the Pirates designated RHP Phil Irwin for assignment. … Nationals 1B Adam LaRoche went 0 for 2 in a rehab start for Class A Potomac on Thursday night. LaRoche has been on the disabled list since May 10 with a strained right quadriceps. LaRoche is eligible to come off the DL on Sunday. … The series continues Friday night when Washington’s Jordan Zimmerman (3-1, 3.70 ERA) faces Pittsburgh’s Charlie Morton (0-6, 3.45).